Compatibility Between Freshwater Tropical Fish

Freshwater tropical fish fall into different groups based on basic compatibility, as not all fish species can cohabitate comfortably without aggression or territorialism. Some freshwater tropical species are naturally more compatible than others, while some species can be housed only with similar species--if any at all. Compatibility is an important consideration when choosing tropical fish species for an aquarium.

  1. Compatibility Types

    • Freshwater tropical fish fall into different compatibility groups based on their ability to get along with other fish, whether larger or smaller. Community fish are generally friendly toward species of the same size or smaller, but not all community fish are universally compatible with one another. Semiaggressive fish are friendly toward fish of the same species but can be aggressive toward certain other species, especially over territory. Aggressive fish are compatible only with larger fish or fish of the same species; otherwise, they can create territory issues and cause harm to one another.

    Community Fish

    • Most small tropical fish--such as neon tetras, white clouds, guppies, corydoras, small plecostamus, ghost shrimp and rasboras--are community fish. These fish do well in small and large groups, and in mixed aquariums with several species in one space. For these fish to cohabitate comfortably, you should provide them with a warm-water environment and at least 15 gallons of space. Because of their relatively small size, these fish are not generally compatible with larger or more aggressive species of fish.

    Tetras

    • Larger tropical fish--such as swordtails, danios, mollies and platies--and larger tetras, such as black skirts, serape, red eye, painted and black neon tetras, are community species, but they do well only in smaller groups, and these fish are not compatible with most other species. Each fish in this group will do best with members of the same species, especially in small schools.

    Semiaggressive Fish

    • Semiaggressive fish include gouramis, barbs, sharks, loaches, angelfish and eels. These mildly aggressive fish are usually compatible with one another as long as there is enough space to avoid territory issues. As these fast-growing fish mature, they will need as many as 29 gallons of aquarium space to maintain the peace. Their space needs will grow as they do, and so their numbers should be kept small. With semiaggressive fish, there is always a potential for aggressive behavior, especially if the fish cannot establish separate territories in the aquarium.

    Aggressive Fish

    • Cichlids are an example of aggressive fish, which naturally prey on other fish over territory issues or for food. New World cichlids, such as Texas cichlids, pink convict, convict, firemouth and Jack Dempsey, are compatible only with one another, or with large community fish capable of defending themselves, such as large plecostomus, catfish and white-tip sharks. Oscars and larger cichlids are compatible only with larger semiaggressive or aggressive fish, and issues may still arise between these species. Red, black, pink and tiger Oscars are especially aggressive and should typically be paired only with similar species, large plecostomus, sharks and pacus.